Multiplex signaling system



Jan. 15, 1924. 4 1,480,612

I H. w. HITCHCOCYK MULTIPLEX SINALING SYSTEM Filed Nov. 12, 1921 4 fiqoealel'jzmion INVENTOR a v v k ATTORNEY Patented Jan. 15, 1924.

umreo STATES 1,480,612 PATENT OFFICE.

HARRY W. HITCHCQCK, OF NEW YORK. N. Y., ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

MULTIPLEX SIGNALING SYSTEM.

Application filed November 12, 1921.

To all whom it may concern.

Be it known that I, HARRY W. Hrron- COCK, residing'at New York, in the county of Bronx and State of New York, have invented certain Improvements in Multiplex Signaling Systems, of which the following is a specification.

This invention relates to transmission circuits and more particularly to telephone 10 circuits upon which carrierchannels may be superposed.

One of the objects of the invention is to simultaneously transmit ordinary voice frequencies andone or more carrier frequencies within the voice range over the same circuit, said carrier frequencies being adapted for the transmission of telegraph signals. This object of the invention, as well as other objects, may beaccomplished by utilizing a transmission circuit of the four-wire type, over each pair of wires of which the telephone frequencies are transmitted in one direction, and the carrier frequencies employed for telegraph transmission are transmitted in the opposite direction, suitable balancing arrangements being provided to discriminate between the oppositely directed transmissions. The invention may be more fully understood from the following description when read in connection with the accompanying drawing, Figure 1 of which illustrates a circuit arrangement embodying the principles of the invention, and Fig. 2 of which illustrates a balancing arrangement used in connection with the circuit of Fig. 1.

Referring to Fig. 1, L is a terminal telephone line adapted to be associated with a four-wire circuit through a hybridcoil 10, and a balancing network N. The fourwire circuit comprises two pairs of wires, each pair being divided in sections at repeater points so that sections such as LW and LVV may beused for transmitting voice frequencies from east to west, while sections such as LE and LE may be used for transmitting voice frequencies from west to east. At the terminal point the section LW, instead of being connected to the terminal line L by a direct bridge across neutral points of the transformer 10. is terminated in a hybrid coil 11 and bala'ncingnetwork NW. The third winding of the hybrid coil is connected Serial No. 514,736.

to the neutral points of the hybrid coil 10 through a onewvay telephone amplifier RW. The hybrid coil 11 is utilized'for the purpose of connecting the: carrier transmitter LW and the network NW at the carrier frequencies,and the details of this network are illustrated in Fig. 2, which will be described later. The filters TF and TF may be ordinary tuned circuits or band filters of the Campbell type.

At the repeater point the one-way repeater RW for the telephone circuit, instead of being connected directly in the line, as is the usual practice with four-wire circuits, is connected'between the line sections LW and LW through twohybrid coil arrangements 12 and 13, the input side of the repeater being connected to neutral points of the main windings of the hybrid coil 12. The line sections LW and LW are balanced by networks N W and NW. This arrangement permits of transmission oftelephone currents from east to west, although the introduction of the hybrid coils, 11, 12 and 13 with the associated balancing networks, involve some transmission loss. This loss maybe made up, however, by working the repeaters at a higher gain.

In order that telegraph signals may be transmitted from west to east over the line sections lid Valid LVV, these sections are interconnected through a telegraph repeater 13,, which may be, for example, a vacuum tube repeater adapted to amplify all of the carrier channels simultaneously. The output circuit of the repeater is divided so that the channels are separated through filters TF, and TF,, th channelsthen being joined to the hybrid coil 13 through the bridged network TX, which will be described later.

The line sections LE and LE are connected for transmission of the telephone currents from west to east in a similar manner, hybrid coils let and 15 with associated balancing networks NE and NE being.

provided, and the telephone repeater RE being connected to these hybrid coils in a manner analogous to that already described, but with the connections reversed so that transmission will take place in the opposite direction. Likewise, the carrier channels may be transmitted from east to west through a telegraph repeater R having selecting devices RF RF,, in its output circuit for segregating the channels, the channels being again combined through the network RX associated with the neutral points ofthe hybrid coil 15.

At the terminal station the line section LE terminates in the hybrid coil 16 and balancing network NE, and carrier telegraph receivers R and R are associated with the third winding of the hybrid coil 16 through filters RF, and RF The terminal line L is associated with line section LE through a one-way amplifier RE,

" whose outputside is connected, to neutral points of the hybrid coil 16, and whose input side-is associated with the third winding'of the hybrid coil 10. i

- Voice currents incoming from. the line L willbe transmitted'through the hybrid coil 10 and amplifier RE to the midpoints of the hybrid coil 16, and thence over the line section LE to the hybridcoil 15. The voice currents applied to the neutral. points of hybridcoil 16 do not react upon the telegraph. receivers R and B, because of the balanced. condition of the circuit at this point. At the repeating station the voice currents transmitted east pass through the hybrid coil 15 to the telephone repeater RE. The amplified currents are then impressed uponneutral points of the hybrid coil 14 for transmission to the line section LE. The circuit being balanced at this point prevents the transmission of the voice currents into the circuit including the telegraph repeater R Telephone currents transmitted from the line section LW in a similar manner pass through the transformer 13, amplifier RVV and hybrid coil 12 to the line section LVt without reacting in the telegraphrepeater R Telephone currents transmitted over the line section LW pass through the hybrid coil 11 and amplifier RW to midpoints of the hybrid coil 10 andthence to the terminal line L. Owing to the balanced condition of the circuit at the hybrid coil 10, the telephone currents transmitted from east to west do not react in the circuit LE-LE.

The carrier frequencies produced by the transmittersT and T are impressed upon neutral points of the hybrid coil 11 and are therefore prevented from passing through the, amplifier RW, but flow over the circuit LVV from west to east in adirection opposite to that of thetelephone currents. At the repeater station the telegraph carrier frequencies pass through the hybrid coil 12 to the telegraph repeater R, and upon being impressed upon neutral points of the hybrid coil 13 are transmitted over the line LTV from west to east. These currents are pre vented from entering the circuit of the telephone repeater RVV owing to the balanced condition of the hybrid coil 13. Similarly, telegraph carrier frequencies within the voice range incoming from the line section LE pass through the hybrid coil 14 and telegraph repeater R to midpoints of the hybrid coil 15,.and thence to the line section LE without reacting in the telephone repeater RE. These currents are transmitted over the line section LE from east to west, and pass through the hybrid coil 16 to the selective circuits RF, and RF,, which select the individual carrier frequencies into the proper channels so that they are receivedby the. receivers R and R The balancing circuits N, Nl/V, N V, NlV, etc., are designed to give as high a degree of balance as possible over the entire operating range and in addition to be balanced exactly for the telegraph currents. The filters such as TF TF TF TF5, and thecorresponding filters used for transmission in the opposite direction, are designed to transmit only currents of the carrier frequency; assigned to each channel, and consequently, the circuit of the telegraph repeater isselective ofthe carrier frequencies; The combination of selective circuits associated with the amplifier and balancing network results in a very. high singing pointsfor all frequenciesand a low crosstalk between the telephone and telegraph system's.

Various arrangements will suggest themselves whereby the networks may be balanced exactly for the telegraph frequencies. One arrangement well adapted for the purpose is illustrated in Fig. 2, which shows in more detail the repeating apparatus for interconnecting two line sections of one side of the four-Wire circuit. The exact balance in this case is attained by inserting between the two halves of the hybrid coil 13 a small reactance 20 and a small resistance 21. The bridged 1 points of the hybrid coil are so arranged that they can be connected to thereactance and resistance at any point. In this way, resistance or reactance may be introduced into either the line or network side of the hybrid coil by changing the position of the contacts. The resistance and reactance need only be as large as the greatest difference in impedance between the line and network which it is desired to balance. Since a set of bridged points may be connected to a selective circuit having a high impedance to every frequency except the one for which it is to be used, itispossible to balance two or' more circuits on the same hybrid coil as Oil indicated in the drawing, the circuits being rendered selective by means of the filters TF TF Since the circuit including the filter TF has a high impedance with respect to the currents which are transmitted through the filters TF the position of the contacts associated with the'filter TF will have a very small efi'ect upon the balance so far as the currents transmitted through TF are concerned. 'By one or two adjustments of these contacts it is possible, therefore, to balance both circuits very closely.

Thearrows on the amplifiers RW and It, in figure may be taken to show that transmission takes place in the direction indicated. Under these conditions the refined balancing arrangement prevents telegraph carrier frequencies from reacting in the telephone circuit. If the one way amplifier be arranged to transmit in the opposite direction, however, the balancing arrangement becomes effective to prevent telephone frequencies which coincide with the telegraph carrier frequencies from producing any reactance in the telegraph circuit.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated without departing from the spirit of the invention as defined in the following claims.

VVhat is claimed is:

1. In a multiplex transmission system, a four-wire circuit comprising two lines, over one of which telephone currents are transmitted in one direction and over the other of which telephone currents are transmittedin the other direction, and means whereby signaling currents within the voice range may be transmitted over each of said lines in a direction opposite that to which the voice currents are transmitted.

2. In a multiplex transmission system, a four-wire circuit comprising two lines, over one of which telephone currents are trans mitted in one direction and over the other of which telephone currents are transmitted in the other direction, means whereby signaling currents within the voice range may be transmitted over each of said lines in a direction opposite to that in which the voice currents are transmitted, and means at terminal points of said lines for separating said signaling currents from said voice currents.

3. In a multiplex transmiss1on system, a four-wire circuit comprising two lines, over one of which telephone currents are transmitted in one direction and over the other of which telephone currents are transmitted in the other direction, means whereby signaling currents within the voice range may be transmitted over each of said lines in a direction opposite that to which the voice currentsare transmitted, and means at terminal points of said lines for separating said signaling currents from said voice currents, said means comprising balanced circuit arrangements. 4. In a multiplex transmission system, a four-wire circuit comprising a pair of lines over'on-e of which voice currents are transmitted in one direction and over the other of which voice currents are transmitted in the opposite direction, repeaters in each of said lines for amplifying voice currents, means associated with said lines whereby signaling currents within the'voice range may be transmitted over said lines indirections opposite to those in which voicecurrents are transmitted, and means atsaid repeater points for separating said voice currents and said signaling curents.

5. In a multiplex transmission system, a four-wire circuit comprising a pair of lines over one of which voice frequencies are transmitted in one direction and over the other of which voice currents are transmitted in the opposite direction, repeaters in each of said lines for amplifying voice currents, means associated with said lines whereby signaling currents within the voice range may be transmitted over said lines in directions opposite to those in which voice currents are transmitted, and means at said repeater points for separating said voice currents and said signaling currents, said means comprising balanced circuit arrangements.

6. In a multiplex signaling system, a four wire circuit comprising a pair of lines over one of which voice currents may be transmitted in one direction and over the other of which voice currents may be transmitted in the opposite direction, terminal circuits with which said lines are associated, trans-,

mitting arrangements and receiving arrangements associated with each line at the terminal points for transmitting signaling currents within the voice range over said lines in directions opposite to the directions in which voice currents are transmitted, a hybrid coil and a balancing network associated with each line at the terminal thereof, connections from said hybrid coils to said terminal circuits and connections from said transmitting and receiving arrangements to said hybrid coils, said connections being conjugate with respect to the connections to the terminal circuit.

7 In a multiplex signaling system, a four wire circuit comprising a pair of lines over one of which voice currents may be transmitted in one direction and over the other of which voice currents may. be transmitted in another direction, means associated with said lines for transmitting signaling currents within the voice range over said lines in di rections opposite to the directions in which voice currents are transmltted, repeater stations associated with said 111168, an amplifier for voice currents and an amplifier for signaling currents at each repeater station, hybrid coils and balancing networks associated with said lines at said repeater stations, and connections from each of said hybrid coils to said amplifiers, said connections being so arranged that the connection to the voice amplifier will be conjugate with respect to the connection to the signaling current am 8. An arrangement for discriminatingbetween the oppositely directed transmissions comprising a transmission line, a balancing network for approximately balancing said transmission line over a range of frequencies, a hybrid coil interposed between said transmission line and balancing circuit, a one-way circuit inductively associated with said line through said hybrid coil, an inductance and a resistance interconnected between the two halves of the hybrid coil, and a plurality of signaling circuits bridged across said inductance and resistance elements at points such that a condition of conjugacy will exist between each of said circuits and said one-way circuit at the frequency used for transmitting over each of said circuits.

In testimony whereof, I have signed my name to this specification this 5th day of November, 1921.

HARRY W. HITCHCOCK. 

